1. Field of the Invention
The present invention relates to a method of testing a fitted state of piezoelectric elements used when manufacturing, for example, a head suspension that is a device arranged in a disk drive of an information processing apparatus such as a personal computer. The present invention also relates to a head suspension manufactured through the test of the fitted state of the piezoelectric elements.
2. Description of Related Art
Small-sized, precision information devices are rapidly advancing, and for use with such devices, needs for micro-actuators capable of conducting positioning control for very small distances are increasing. The micro-actuators are highly needed by, for example, optical systems for correcting focuses and inclination angles, ink-jet printers for controlling ink heads, and magnetic disk drives for controlling magnetic heads.
The magnetic disk drives increase storage capacity by increasing the number of tracks per inch (TPI), i.e., by narrowing the width of each track on a magnetic disk.
Large-capacity magnetic disk drives, therefore, need an actuator capable of precisely positioning the magnetic head within a minute range across tracks.
To meet the need, in Japanese Unexamined Patent Application Publication No. 2010-86649, a head suspension employing a dual actuator system is disclosed. The dual actuator system uses a piezoelectric element in addition to a usual voice coil motor that drives a carriage to which the head suspension is attached.
FIG. 23A is a plan view roughly illustrating the head suspension, FIG. 23B is an equivalent circuit of the piezoelectric elements, and FIG. 23C illustrates deformation of the piezoelectric elements.
In FIG. 23A, the head suspension 101 has a base plate 103, a load beam 105, and a pair of piezoelectric elements 107a and 107b. The piezoelectric elements 107a and 107b are arranged in opposite polarity to form an actuator 109. A front end of the load beam 105 supports a read/write head 111. The load beam 105 and head 111 form a movable member.
In FIG. 23B, the piezoelectric elements 107a and 107b deform according to a voltage applied thereto. Namely, depending on the applied voltage, the piezoelectric elements 107a and 107b oppositely deform in expanding and contracting directions as illustrated in FIG. 23C. As a result, the head 111 slightly moves relative to the base plate 103 through the load beam 105 in a sway direction, i.e., a direction in which the piezoelectric elements 107a and 107b are arranged side by side.
To precisely allow such a minute movement of the head 111, the piezoelectric elements 107a and 107b must precisely be fitted to the head suspension 101 as designed.
It is difficult, however, to distinguish the piezoelectric elements 107a and 107b and the top and bottom faces thereof by appearance. Due to this, there is a possibility of erroneously fitting the piezoelectric elements 107a and 107b to the head suspension 101.
To avoid this, there is a technique of providing the piezoelectric element 107a (107b) with a mark so that the piezoelectric elements 107a and 107b are distinguishable by appearance. This technique, however, raises a contamination problem, and therefore, is hardly adoptable.
There is another technique that applies a voltage to the actuator 109, measures an actual stroke of the head 111, and determines whether or not the piezoelectric elements 107a and 107b are correctly fitted to the head suspension 101.
An actual stroke of the head 111 is very small such as 50 to 100 nm, and therefore, is measurable only with a precise measuring device that is very expensive.
There is still another technique disclosed in U.S. Pat. No. 6,639,411. This technique forcibly displaces the head suspension 101, and according to signals obtained at this time, determines orientation of the piezoelectric elements 107a and 107b and whether or not the piezoelectric elements are correctly fitted to the head suspension 101.
FIG. 24A is a view roughly illustrating the head suspension 101 of FIG. 23A installed in a hard disk drive and FIG. 24B is a view illustrating the head suspension 101 supported alone in a free state.
As is apparent from comparison between FIGS. 24A and 24B, the head suspension 101 supported alone differs from the head suspension 101 that is installed in a hard disk drive and receives load on the load beam 105. When the head suspension 101 supported alone receives oscillation for a test, the load beam 105 of the head suspension 101 unstably moves to provide unstable data. With such unstable data, it is unable to correctly determine a fitted state of the piezoelectric elements 107a and 107b of the head suspension 101.
In addition, the related arts mentioned above hardly test a breakage in wiring connected to the actuator 109.